package Concurrency;


/**
 * Fork/Join框架
 * 用于并行执行任务的框架,是一个把大任务分割成若干
 个小任务,最终汇总每个小任务结果后得到大任务结果的框架
 */

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.Future;
import java.util.concurrent.RecursiveTask;
public class CountTask extends RecursiveTask<Integer> {

    private static final int THRESHOLD = 2;  // 阈值
    private int start;
    private int end;
    public CountTask(int start, int end) {
        this.start = start;
        this.end = end;
    }

    @Override
    protected Integer compute() {
        int sum = 0;
// 如果任务足够小就计算任务
        boolean canCompute = (end - start) <= THRESHOLD;
        if (canCompute) {
            for (int i = start; i <= end; i++) {
                sum += i;
            }
        } else {
// 如果任务大于阈值,就分裂成两个子任务计算
            int middle = (start + end) / 2;
            CountTask leftTask = new CountTask(start, middle);
            CountTask rightTask = new CountTask(middle + 1, end);
// 执行子任务
            leftTask.fork();
            rightTask.fork();
// 等待子任务执行完,并得到其结果
            int leftResult=leftTask.join();
            int rightResult=rightTask.join();
// 合并子任务
            sum = leftResult + rightResult;
        }
        return sum;
    }


    public static void main(String[] args) {
        ForkJoinPool forkJoinPool = new ForkJoinPool();
// 生成一个计算任务,负责计算1+2+3+4
        CountTask task = new CountTask(1, 4);
// 执行一个任务
        Future<Integer> result = forkJoinPool.submit(task);
        try {
            System.out.println(result.get());
        } catch (InterruptedException e) {
        } catch (ExecutionException e) {
        }
    }
}
